As illustrated in FIGS. 1 and 2, a prior art thin film transistor TFT includes a gate electrode 100, a gate insulating layer 200, an active layer 300 and a source/drain layer 400 successively stacked from top to bottom on a substrate. A channel is formed between the source electrode and the drain electrode. The gate electrode 100 of TFT is connected with a gate line 500 on the array substrate, and the source electrode of TFT is connected with a data line 600 on the array substrate. As illustrated in FIG. 2, the gate electrode 100 of the prior art TFT is located at the bottom of the channel and influences the channel only from the bottom. Only one drain electrode current channel is formed after the TFT is turned on. Therefore, prior art TFTs have a low ON current Ion, a low opening ratio and high ON voltage and load.